<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>07</title>
    <style>
        .item{
            float: left;
            width: 280px;
            height: 170px;
            border: 1px solid red;
        }
    </style>
</head>
<body>
<span>LEFT</span>
<span style="float: right">RIGHT</span>


<div style="background-color: purple">
    <!--这样就脱离文档流了-->
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
    <div class="item"></div>
<!--    <div style="clear: both"></div>-->
</div>
<div>你好啊！</div>
</body>
</html>